1. Field of the Invention
The present invention relates to a conductive polymer gel and its application for driving a miniature actuator. In particular the present invention is drawn to a polythiophene-based conductive polymer gel used to open and close an actuator valve.
2. Background and Related Art
Current trends in the designs of analytical instrumentation, especially where fluids are used to carry analytes to various instrument stations for processing (such as separation, mixing, species detection, and the like), are increasingly tending toward integrated and miniaturized systems. However, it is generally recognized that these designs will only be possible with the development of fast and efficient micro-actuators that can be operated as pumps and valves. As analytical equipment is scaled down the mechanical structures comprising these devices must also decrease in size. As is often the case, however, such macroscopic designs are not easily scaled down and replicated as microdevices and still providing acceptable function. Thus there is a need for development of microscopic xe2x80x9cmachinesxe2x80x9d having useful performance characteristics. In this regard conductive polymers lend themselves well to such designs.
The basic premise of the present invention is to use a conductive polymer gel having the property of changing dimension upon application of a small electrical potential, typically less than 1 volt, as a value in an actuator. The expansion and contraction of a body comprising the polymer gel results from a potential induced change in the oxidation state of the polymer and the associated diffusion of charge balancing ions and their coordinating solvent into and out of the gel (FIG. 1). As the polymer is oxidized, it forms positive charges that reside on the xe2x80x9cbackbonexe2x80x9d of the polymer chain. As solvent coordinated anions diffuse into the polymer to balance the charge, the dimensions of the sample increase as the result of osmotic pressure developed during the influx of the two species, and result in an effect that can be harnessed to produce useful work.
While a large body of prior art exists describing electrochemically driven swelling/de-swelling of conductive polymers none of the work in the literature has reported the direct measurement of the mechanical response of these materials to electrochemical stimulation. Neither is there any mention of the use of the work-producing effect of the response of these polymer gels to the application of small electrical potentials. Presumably, therefore, none have recognized the potential use of these materials as control members in micro-actuators.
Beginning in the late 1980""s with Murthy, et al., (J. Chem. Phys. (1987), v. 87, pp. 2346) and more recently with Li and Aoki, (J. Electroanal. Chem. (1998), v. 453, pp. 107; Kaneko and Kaneto, (Synth. Met. (1999), v. 102, pp. 1350); Madden, et al., (Synth. Met. (1999), v. 105, pp. 61); and Otero and Bengoechea, (Langmuir (1999), v. 15, pp. 1323), a large body of work developed that described electrochemically driven swelling/de-swelling of conductive polymers. Our interest in these materials stems from their potential use as small-scale actuators, valves or pumps in microsystems applications. A much smaller body of art has reported measurements of the tensile forces (see, for instance, Chen, et al., Macromolecules (2000), v. 33, 1232) and shear modulus generated in pre-loaded thin films (Chen and Inganxc3xa4s, Synth. Met. (1995) v. 74, 159).
In the present invention, the free extension, or closure forces (pressures), generated by these materials when they are confined, is characterized in an unambiguous manner. This work describes the synthesis of a polythiophene-based conductive polymer gel actuators. Measurements of gel extension and force in one axis under an applied square wave electrical stimulating pulse is shown.
It is therefore an object of this invention to provide a conductive polymer gel responsive to low electrical potentials.
It is another object of the invention to provide an actuator comprising said conductive polymer gel.
Yet another object of this invention is to provide a polythiophene polymer gel which is responsive to electrical potentials of less than xc2x11 volt.
Still another object of the invention is to provide a polymer gel actuator generating an axial pressure of about 2 pounds-force per square-inch under the influence of a +0.8 volt potential.